Resident Population in Mercer County, NJ was 381.67100 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Mercer County, NJ reached a record high of 386.44100 in January of 2020 and a record low of 304.11600 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Mercer County, NJ - last updated from the United States Federal Reserve on May of 2024.